Recently, a switch duplexer having a small size and high performance is demanded increasingly for use in mobile phone. A conventional circuit configuration of an conventional switch duplexer for dual bands is shown in FIG. 14. A circuit configuration of the switch duplexer in a composite terminal for mobile phone systems called GSM in a 900 MHz band and DCS in a 1.8 GHz band, both of which are in service in Europe at present time.
In the diagram, reference numerals 1001 to 1005 denote input/output ports, reference numerals 1006 and 1007 denote control terminals, reference numerals 1008 to 1011 denote diodes, reference numerals 1012 and 1013 denote transmission lines, reference numerals 1014 and 1015 denote band-pass filters (BPFs), and reference numeral 1016 denotes a diplexer. Diplexer 1016 is generally composed of circuits combined with low-pass filter (LPF) 1016a and high-pass filter (HPF) 1016b. 
In this circuit configuration, an antenna (not shown) is connected to input/output port 1005, and the signal received by the antenna is first distributed into GSM signal and DCS signal by diplexer 1016. The length of transmission lines 1012 and 1013 are set at one-quarter wavelength for the frequency bands of GSM and DCS, respectively. When a positive voltage is applied to the control terminal 1006 where a current flows accordingly, diodes 1008 and 1010 are turned on, and ports 1005 and 1001 are thus coupled each other. Similarly, when a positive voltage is applied to the control terminal 1007 where a current flows accordingly, diodes 1009 and 1011 are turned on, and ports 1005 and 1003 are thus coupled. If a voltage is not applied to control terminals 1006 or 1007, diodes 1008 to 1011 are turned off, and ports 1005 and 1002 are thus disconnected, and ports 1005 and 1004 are thus disconnected.
Ports 1001 and 1003 operate as transmission ports (Tx). BPFs 1014 and 1015 operates as filters for limiting a receiving bandwidth. Ports 1002 and 1004 operates as reception ports (Rx).
In such conventional configuration, four diodes are required. Since having larger sizes than other circuit components such as L and C, the diodes have not been integrated into a laminated body, and thus the device is hardly reduced in size. The diodes are more expensive than the other circuit components and thus increases the cost of the device. Besides, the switch duplexer for both GSM and DCS requires a couple of transmission lines 1012 and 1013, which also have the duplexer hardly reduced in size.